Protective means for electric circuits



Aug. 26 1924.

G. H. STEVENSON PROTECTIVE MEANS FOR ELECTRIC CIRCUITS Filed May 25 1921 //7ve/7 far.-

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Fir 1T; HEATING CIRCUIT kzummzu 55m 6 m F Patented Aug. 26, 1924.

UNITED STATES PATENT OFFICE. I

GEORGE E..STEVENSON, OF RYE, NEW YORK, ASSIGNOR TO WESTERN ELECTRIC COM- PANY, INCORPORATED, OEF NEW YORK,

N. Y., A CORPORATION OF NEW YORK.

PROTECTIVE MEANS FOR ELECTRIC CIRCUITS.

Application filed May 25,

To all whom it may concern."

Be it known that I, GEORGE H. STEVEN- SON, a subject of the King of Great Britain,

g having taken out first papers in the United States, residing at Elmwood Avenue, Rye, in the county of Westchester, State of New York, have invented certain new and .use-

ful Improvements in Protective Means for Electric Circuits, of which the following is a full, clear, concise, and exact description.

This invention relates to protective means for electric circuits and more particularly it relates to protective means for high frequency or radio circuits in which vacuum tubes of the 3-electrode type are employed for amplifying, modulating, generating or detecting signaling currents.

As is we'l-known in the art vacuum tubes of the 3-electrode type comprise an anode,

a cathode and a grid or control electrode for controlling the space current between the other two electrodes. These tubes are designed to work between certain limits of anode-cathode space current and a variation of the space current outside the permissible range is highly undesirable particularly if the current at any time exceeds the allowable maximmn, for in such case the tube is liable to blue haze or bow up or otherwise be rendered useless. The intensity of the space current for a given tube depends firs t, upon the anode-cathode potential; second, upon the value of the voltage supplying the heating current for the cathode; and third, upon the potential'of the grid with respect to the cathode. The variation of any one of these voltages beyond its permissible range of variation may be sufiicient to-increase the space current to such an extent that the tube will be completely destroyed or rendered useless. To prevent such a possibility is particularly important in signaling circuits .such as radio circuits wherein high power vacuum tubes capable of handling from .1 kilowatt to one kilowatt or more of output power are employed which are generally worked with almost the maximum allowable space current to obtain the greatest amount of poweroutput therefrom.

In accordance with this invention means are provided responsiveto variations in the space current of such a tube to render the tube inoperative whenever the space cur- 1921. Serial No. 472,365.

rent tends to increase beyond the desired range. lln the preferred form of this invention a 2-electrode tube with a filamentary cathode and an anode is employed having its cathode connected in the anodecathode circuit of the tube to be protected and having its anode-cathode circuit competed through a source of voltage and the solenoid of a relay which when energized serves to disconnect from the tube to be protected one of its energizing sources of voltage. Such an arrangement is especially advantageous in radio or other ultra-audio frequency signaling circuits, since such protective means does not require the insertion of an inductance element such as a winding of a relay or electro-magnet in any part of the high frequency circuit of the tube to be protected. Such an insertion would be quite objectionable since it would seriously affect the tuning of the high frequency circuits,

which are generally of a highly selective nature.

This invention will be better understood by reference to the following detailed description taken in connection with the accompanying drawings in which Fig. 1 represents an embodiment of this invention 1n .which the .Z-electrode tube responsive to changes in the space current of the tube to be protected, controls a solenoid for-disconnecting from the tube to be protected its source of space current; while Fi 2 represents a modification of Fig. 1 in which a solenoid controls the connections of the source'of voltage for supplying heating current to the cathode of the tubes to be protected. Fig. 3 illustrates acurve showing the value of the space current in a 2- electrode tube for difierent values of the heating current for its cathode.

Referring more particularly to Fig. 1, a

radio transmitting system is disclosed there-' in which is adapted to supply to the antenna 10'high frequency oscillations modu lated in accordance with the signalling oscillations from the transmitter 11. The principal features of this radio transmitting system have been described in detail in a publication by Craft and Colpitts in an article on Radio Telephony published in vol. 38, page 360 of-the American Insti tute of Electrical Engineers. For the purposes of this specification the system may be briefly described as comprising two vacuum tubes 12 and 13 connected in parallel and acting as a source of ultra-audio frequency oscillations which may be, for example, of the order of one million cycles per second. Vacuum tubes 14 and 15 are two amplifiers connected in parallel having their common input circuit associated with the transmitter 11 by a transformer 16 and their output circuit so associated with the generators 12 and 13 that the tubes 12 and 13 act both as generator and modulator tubes. The high frequency oscillations from tubes 12 and 13 modulated in accordance with the signals from source '11 are impressed on the antenna 10 by the transformer 17.

Tubes 12, 13, 14 and 15 which are of the well-known 3-electrode type comprise cathodes 18, 19, 20 and 21; anodes 22, 23, 2-1 and 25 and control electrodes 26, 27, 28 and 29, respectively. The four cathodes are supplied 'n parallel with heating current from a common source of voltage or battery 30. 31 is a DC generator or other source of voltage for supplying the desired anode-cathode voltage for these four tubes. The connection of one side of generator 31 to the cathodes 18 to 20 inclusive may be traced through conductors 32, 33 and 34 to each of the cathodes. The other side of generator 31 is connected to anode 24 by conductor 35, movable contact 36 of relay 37, conductors 38, 39, cathode 40 of a 2-electrode tube 41 to anode 24. The connection of generator 31 to anode 25 may be traced through movable contact 36, the cathode 42 of the .Z-electrode tube 43. The connection of the generator to anodes-22 and 23 may be similarly traced through the cathodes 45, 46 of the two 2-electrode tubes 47 and 48 respectively. From these connections it is apparent that the space cu'rrent flowing through each of the 3-electrode tubes must traverse the filamentary cathode of one of th 2-electrode tubes. Each of the 2-electrode tubes 41, 43, 47 and '48 should be so designed, when its corresponding 3-electrode tube is traversed by its normal average space current, that the electron emission of the cathode of each 2-electrode tube will be only a fractional part of its maximum electron emission. Referring to Fig. 3 the curve 49 illustrates the various values the electron emission in the cathode will have when its heating current is varied. In this figure the ordinates represent various values of space current and the abscissae represent various values of the filament heating current. Each of the 2-electrode tubes should be preferably'so designed that when its cathode is traversed by the normal space current of its tube to be protected that the space current of the 2-e lectrode tube has a value approximately corresponding to the value where the dotted line. in- 'tersects curve V 49. If such an adjustment is made it can be readily seen that a small change in the heating current of the cathode will produce a much greater change in the space current of the 2-electrode tube.

The 2-electrode tubes 41, 43, 47 and 48 are supplied with space current from a common source of voltage 50. One side of sourc of voltage 50 is connected to-catl1odes 42,45 and 46 by leads 35, 38, while the other side of this source is connected to the anodes 51, 52, 53, 54, by relay winding 55, lead 56, relay winding 57 and lead 58, relay Winding 59 and lead 60, and-relay winding 61 and lead 62 respectively. Relay 55 should be so adjusted that its contacts will remain open as long as tube 14 is supplied with normal space current. WVhen, however, the circuit conditions of tube 14 should so change that the space current thereof exceeds the allowable maximum, the

heating current of cathode 40 will thereby be increased, which will produce a much greater increase in the space current of tube 41 which flows through relay 55. This increase in the space current of tube 41 should be sufiicient to cause relay 55 to pull up its movable contact 63. The closing of movable contact 63 energizes relay 37 from battery by closing the circuit from battery, winding relay 37 ,conductor 64, movable contact 63 and conductor 65 to the other side of the battery and relay 37. In pulling up its contact 66, the relay locks itself up over a circuit completed by the key 67 and will remain locked up until key 67 is manually operated. Relay 37 also pulls up its movable contact 36 to disconnect generator 31 until the system has been personally supervised by an attendant to correct the defect in the system which resulted in the objec tionable increase in the space current of tube 14.

. In the same manner if the space current of tube 15 should be increased beyond its allowable maximum the 2-electrode tube 43 will cause relay 57 to pull up its movable contact thereby energizing relay 37 to disconnect the source of voltage 31. Relays 51 and 60 will operate similarly in response to increases in the space current of tubes 12 and 13 respectively.

The modification illustrated in Fig. 2 is somewhat similar to that of Fig. 1 except that a switching relay 70 is provided for disconnecting the source of voltage 30 from the cathodes of the tubes 12 to 15 whenever their space current exceedsthe allowable maximum. Each of the tubes 12 to 15 has associated therewith one of the 2i-electrodetubes 71, 72, 73 and 74, the

current from the associated 3'-electrode tube. Instead of providing a relay individual to each 2-electrorle tube as in ig. 1 for controlling the relay which disconnects the source of voltage, the system ofFig. 2 employs a single relay 75 common to the four 2-elctrode tubes 71 to 74 inclusive. Whenever the space current of one of the 2-electrode tubes is increased due to an undesirable increase in the space current of its corresponding 3-electrode tube, relay 75 obvious connections will be energized to pull up its movable contact 76 and energize the relay 70 which serves to break the connections between the cathodes and their source of heating current 30.

The above described arrangement for regulating a 3-electrode tube by a 2-electrode tube which has its cathode traversed by space current of the 3-electrode tube is es pecially advantageous in ultra-audio frequency circuits, since such regulating means does not. require the insertion of an inductance element such as a winding of a relay ina circuit traversed by alternating currents of ultra-audio frequencies. Inasmuch as a filamentary cathode such as 46 of tube 48 is substantially non-inductive, the insertion of such a cathode in the output circuit of tube 13 does not interfere with the oscillatory character of the output circuit, such as changing the tuning thereof.

Although this invention has been described above in connection with an ultraaudio circuit it is to be understood that this invention may be beneficially employed in other types of circuits employing evices to be protected from excessive currents or voltages. It is also to be understood that methods within this invention other than those specifically describedabove may be employed if desired for rendering the ifselectrode tubes inoperative whenever their space current tends to increase beyond the allowable maximum.

What is claimed is: v 1. In combination, a vacuum tube having an anode and a cathode, a second vacuum tube having a filamentary cathode and a second electrode, a source of voltage for said first tube, and external connections for said second cathode, said external connections being connected in series with said anode, said first cathode and said source.

2. In combination a vacuum tube having an anode and a cathode, a second vacuum tube having a filamentary conductor therein and a second electrode, a source'of voltage, and connections between said source and said anode and cathode, one of said connections including said filamentary conductor.

3. In combination a vacuum tube having an anode and a cathode, a second tube having an anode and a cathode, a common source of voltage for supplying space current'to said first tube and supplying heating current to said second cathode, and a second source ofvoltage for supplying space current to said second tube.

4. Incombination, a vacuum tube having an anode, a cathode and a control electrode, a second vacuum tube having a plurality of electrodes, one of which has a plurality of external terminals, ,a connection between said anode and one of said terminals and a connection between said cathode and another of' said terminals. 7

5. In combination, a vacuum tube having an anode and a cathode, a source of voltage, an electron discharge path, and connections from said source for supplying heating current to said cathode, one of said connections being made through said electron discharge path, whereby the heating current supplied to said cathode flows through'said discharge path.

6. In combination a vacuum tube having an anode and a cathode, a source of space current for said tube, a. second vacuum tube havin an anode and a cathode, connections where y. the. temperaturenofsaid second cathode is responsive to the space current of said first tube, and a work circuit responsive to the resulting changes in the space current of said second tube.

7. In combination, ond vacuum tube having an anode and a cathode, a source of heating current for said cathode, connections whereby the heating current of said cathode is made responsive to variations in a characteristic of said first tube, and means responsive to the resulting changes in the space current'iof said second tube for regulating said first tube.

8. In combination, a vacuum tube, a. second vacuum tube having an anode and a tube for rendering said first tube inoperative.

9. In combination, a vacuum tube, asource of voltage for said tube, a second vacuum 'tube having an anode and acathode, means for making the heating current supplied to said cathode responsive to chan es in a characteristic of said first tube, an an electro-magnetic switch responsive to the resulting change in the space current of said second tube for disconnecting said source from said first tube.

10. In combination, a vacuum tube comprising an anode and a cathode, a second vacuum tube having an anode and a cathode, means whereby heatin current for said second cathode is depen ent upon the anodecathode current of said first tube, a solenoid connecting said source traversed by space current from said second tube and circuit connections for said first tube controlled by said solenoid.

11. In combination, a vacuum tube having an anode, a cathode and a control electrode, a source of space current for said tube, means for supplying signaling potentials to said control electrode, and a second vacuum tube responsive to variations in a characteristic of said first tube for rendering said first tube inoperative.

12. In combination, a vacuum tube having an anode and a cathode, a second vacuum tube having'a plurality of electrodes, means for controlling the temperature of an electrode of said second tube in response to variations in a characteristic of said first tube, and means responsive to changes in sailde temperature for regulating said first tu 13. In combination, a vacuum tube having an anode and a cathode, a second vacuumtube having an anode and a filamentary cathode, connections for causing the space current of said first tube to traverse said filamentary cathode for heating the same, said connections being such that the electron emission from said filamentary cathode is only a fractional portion of its maximum emission for a given anode-cathode voltage and meansresponsive to the discharge characteristics of said second tube for controlling said first tube.

14.. In combination, a vacuum tube having an anode, a cathode, and a control electrode, a source of voltage for said tube, means for supplying signaling potentials to said tube, a non-inductive element responsive to a condition of said tube, and means responsive through the intermediary of said element to an excessive current in said tube for disfrom said tube.

15. In combination, a vacuum tube having an anode, a cathode and a control electrode, means for supplying to said tube signaling potentials to be repeated, a non-inductive element traversed y current varying in intensity in res onse to variations in a characteristic of said tube, and means operating u on an increase in the current through said e ement for rendering said tube inoperative.

16. An ultra-audio. frequency system comprisin a vacuum tube having an anode, a catho e and a control electrode, a second vacuum tube having a cathode traversed by heatin current of an ultra-audio frequency de on out upon a characteristic of said first tu and means responsive to said second tube for regulatin said first tube.

17. An ultra-audio fre uency system comprising a vacuum tube aving an output circuit, a source of space current for said tube, connections for causing said output circuit to be traversed by currents of an ultra-audio frequency, a second tube having mousse an anode and a filamentary cathode, said cathode being serially connected in said out put circuit whereby the electron emission of said cathode is responsive to variations in the space current of said first tube, and means responsive to variations in the electron emission of the cathode of said second tube for controlling the circuit connections of said firsttube.

18. In combination, a plurality of vacuum tubes each having an anode, a cathode and a control electrode, a common source of space current for said tubes, and a twoelectrode tube responsive to a condition of one of said first tubes for rendering all of said first tubes inoperative;

19. In combination, a plurality of vacuum tubes, each comprising an anode, a cathode and a control electrode, a common source of space current for said tubes, at common source of heating current for said cathodes,

and an additional vacuum tube res onslve to a condition of only one of said tu' es for controlling the condition ofall of said first tubes.

20. In combination, a plurality of vacuum tubes each having an anode, a cathode and a control electrode, a common source of space current for said tubes, a common source of heating current for said cathodes, an additional vacuum tube having-a cathode traversed by heating current varying in accordance with a condition of one of said first tubes, and means responsive to said ad ditional tube for disconnecting one of said sources from all of said first tubes.

21. In combination a plurality of tubes each having an anode, a cathode and a control electrode, an additional vacuum tube individual to each of the first set of tubes and responsive to a condition of its associated tube of the first set and means responsive to one of said additional vacuum tubes for controlling said first-mentioned tubes.

22.. In combination, a vacuum tube, means for supplying alternating currents to said tube, a second vacuum tube, connectionsbetween said tubes for causing a chan e in a condition of said first tube to pro uce a greater chan in a condition of said second tube, and a c1rcuit interrupter controlled by said second tube.

23. In combination, a plyin high frequency waves modulated by signa s to said line, and means responsive to said modulated waves for determining when said modulated Waves will be transmitted to said line. Y

24. In combination, a line, means for supplying high frequency waves modulated by signa s to said line, and a circuit interrupter responsive to a condition of said Waves for determinin .when modulated waves will be transmitte to said line.

25. In combination, a line, means for supline, means for supplyin high frequency waves modulated by signa s to said line, a vacuum tube energized by said waves, and a circuit interrupter controlled by said tube for determining when modulated waves will be transmitted to said line,

26. A system comprising a plurality of tubes and a power supply in common thereto in combination with means individual to each tube actuated by excessive space current through that tube to cut ofi the power supply of the entire system.

27. A signaling system comprising a plurality of vacuum tubes, a common source or energizing current for said tubes, means individual to each tube and actuated when abnormal conditions are present in each tube 1 and means responsive to said first means for rendering all of sad tubes inoperatlve.

1,506,275.-Ger CIRCUITS.

two each In combination, a vacuum tube having an anode and a cathode, means for supplying energizing current to said cathode, means for supplying space current between said anode and cathode and means responsive to an excessive space current for rendering one of said means inoperative.

29. In combination, an electric discharge device having an anode and a cathode, a source of current for heating said cathode, a source of current for supplying space current between said anode and cathode and means responsive to excessive current in said device for disconnecting one of said sources In witness whereof, I hereunto subscribe my name this 19th day of May- A. D., 1921.

GEORGE H. srrivnnson.

. msoLAua/izn,

e H, Stewnson, Rye, N. Y Prorncrrvn MEANS roe-Emerald atent dated August 26, 1924. Disclaimer filed patentee, assignee, Wcstem Electric ,Uompany,

May 5,1926, by the Incorporated, consenting.

Hereby enters this, disclaimer to the said claims of said Letters Patent which are in the following words, to wit:

' 28. In combination, avacuum tube having an anode and a supplying energizing current to said cathode,

I cathode, means for I means :tor supplying space current between said anode and cathode and means responsive to an excessive'space current for render ng one of said means inoperative.

- 29. In combination, an electrlc discharge device having an anode and a cathode,

a source of. current for heating said cathode, space current between sald anode and ca a source of current for supplying thode and means responsive to excessive current in said device for disconnecting one of said sources [Ofici'al Gazette Mag 18, 1926.] 

